The present invention is directed to an electric lamp and more particularly to a parabolic aluminized reflector (PAR) lamp and a method of making a PAR lamp.
A PAR lamp typically includes a light source, such as a tungsten halogen capsule, mounted in a pressed borosilicate glass reflector with a reflective coating applied to the inner parabolic surface. A pressed glass lens usually covers the front aperture and contains optical elements to give the desired beam shape. General service PAR lamps usually have a neck region between the parabolic section and a screw base used for electrical connection to a line current. The neck region provides mechanical support between the reflector optical portion and the base electrical portion. The neck region also provides room for the lamp capsule, leads, capsule mounting components, electrical wiring, and separates the filament from the base to reduce base temperature.
A conventional PAR lamp is shown in FIG. 1. The lamp 10 includes a lamp capsule 12, a reflector 14 having a neck region 15, a base 16, metal eyelets 18, and a lens 20 that encloses capsule 12 in reflector 14. Capsule 12 may be a press-sealed halogen lamp capsule with leads 22 that extend through respective passageways 24 opening to a heel 26 of the reflector 14. The eyelets 18 are in the passageways 24 and grip the leads 22 to hold the capsule 12 in the reflector 14. Alternatively, ferrules, ceramic or cement may be used instead of the eyelets 18 to hold the capsule in the reflector. The reflector 14 may be a glass shell that is preferably a body of revolution with an interior side 28 coated with a reflective coating. The base 16 includes respective, electrically separated, terminals 30 for the lamp. The leads 22 are attached to the respective terminals with wires 32.
With reference now to FIG. 2 that depicts a series of steps in the manufacture of a conventional PAR lamp, the lamp is assembled by inserting the eyelets 18 and then inserting the capsule 12 from the front aperture of the reflector and attaching capsule leads at the reflector heel by means of the eyelets 18. The capsule 12 is supported solely by crimping both of the leads 22 in the eyelets 18 that are compressed into the passageways 24. Automated assembly of the eyelets and capsule into the reflector requires very tight tolerances for the dimensions and placement of the passageways. These tight tolerances increase the cost of the reflector.
In another common PAR lamp construction, the capsule is supported on a metal disk that rests on a shelf in the reflector neck region. Axial movement of the capsule and disk assembly is prevented by crimping metal eyelets to the capsule leads near the heel, pulling the capsule and disk assembly tight to the shelf. The support disk construction does not require the tight passageway tolerance, but the added metal disk and more complex assembly increases manufacturing cost.
Much of the light entering the neck region of PAR lamps is lost due to multiple reflection and absorption by the mounting and capsule components and does not contribute to the beam. It is well known that the cross-sectional area for the capsule inside the reflector should be as small as possible to maximize beam intensity and lamp efficiency (as defined by lamp lumens divided by source lumens). However, both inner and outer surfaces of the reflector must have a suitable draft angle for removal from a mold. The pressed glass reflector therefore commonly used for PAR lamps typically has a minimum draft angle of 3 degrees but in practice, a 5-degree draft angle is typically used. The neck region must also have adequate diameter to fit the capsule mounting devices. When the capsule is supported solely by the leads crimped by the eyelets, the neck region inner diameter must be large enough to make space for the flared ends of the eyelets. This increases the neck region diameter. The flares also require a flat surface on which to seat, which, in turn, creates snag points when the capsule is inserted. Some of the lead ends catch on the flat surface, resulting in failed insertions and causing the product to be scrapped.